The prohibition of the use of force constitutes a cornerstone of the Charter of the United Nations and of present-day international law at large. This prohibition is also widely claimed to be a peremptory norm of general international law (ius cogens). However, the details and implications of this claim remain contested. This regards the exact scope of the peremptory norm in the international law on the use of force and the relationship between the prohibition and its established exceptions (self-defence, security council authorisation, invitation). In addition, the legal consequences and practical implications of a peremptory norm in the ius contra bellum are often ignored, especially when it comes to identifying new trends or changes to the ius contra bellum.
Seeking to clarify these questions, the project can take into account the recent work of the International Law Commission (ILC) on peremptory norms of general international law (ius cogens). The ILC’s conclusions address the identification and legal consequences of peremptory norms. In the annex to the conclusions, the ILC included the prohibition of aggression as a norm it had previously identified as having peremptory status. This has not resolved the issue, given the claim by many states and scholars that the peremptory norm in the ius contra bellum also covered the use of force short of aggression.
Against this background, the aim of the project is threefold. In a first step, it provides a critical appraisal of the ILC’s conclusions on how to identify peremptory norms and what legal consequences they have. This will provide the methodology for the project’s second aim: Identifying the peremptory norm in the ius contra bellum and clarifying the relationship between prohibition and exceptions. The focus will be an analysis of a wide range of instances in which States expressed their views on these issues. In a third step, the implications of the peremptory norm in the ius contra bellum will be scrutinized.